The web splicer of a corrugator is used to facilitate continuous operation of the web end. Corrugated board is comprised of three layers of paper including a top liner, a fluted medium and a bottom liner. A pair of top liner roll stands is located on the upstream side of a single facer that is used to bond the top liner web to the glued flute tips of a fluted medium paper. The medium enters the singlefacer from one of a pair of medium roll stands located downstream of the single facer. In a typical corrugated wet end operation, the medium is unwound from a roll stand, preconditioned with application of heat and steam and then fluted between a pair of corrugated rolls. The fluted medium, conforming to the flute profiles of one of the corrugated rolls, has a starch adhesive applied to the flute tips. The glued flute tips of the medium then come into contact with the top liner directly beneath a pressure roll or pressure belt system where a green bond forms between the liner and medium. This bond is facilitated by the preheating of the top liner after it unwinds from one of the pair of top liner roll stands.
The single face web, comprised of the top liner glued to the fluted medium, progresses down the corrugator bridge to a glue machine. The singleface web has a starch adhesive applied to the bottom flute tips at the glue machine. A bottom liner unwinds from one of a pair of roll stands located at the doublefacer roll stand position. The bottom liner is preheated after which it enters a doublefacer hot plate system. The singleface web with glued flute tips then also enters the doublefacer where it is pressed into intimate contact with the bottom liner on the hot plate by a weighted corrugated belt. The starch is cured by heat as the corrugated web proceeds through the doublefacer and then into the dry end of the corrugator. At the corrugator dry end the web is slit to desired widths according to an order set-up schedule and then cut to desired length by a cutoff knife. The slit and cut sheets are then stacked by a downstacking system.
It is very important to maintain the corrugator process as continuous, even during paper roll change over, to avoid substantial waste and downtime on the corrugator. If the corrugator were stopped for paper roll change, the starch bonding process at both the singlefacer and doublefacer would be interrupted creating substantial waste board. The start-up process is also problematic because of severe warp and loose spots that can cause jam-ups in the corrugator dry end.
To make the process continuous, automatic web splicers are used at the top liner, medium and bottom liner roll stand positions. The splicer is positioned above a pair of roll stands at each position. The predominant splicer technology used for splicing of corrugated web is a “zero speed” splicer. With this type of splicer, the paper of the expiring roll and the paper on the new roll are spliced by bringing the tail of the expiring roll web to zero speed.
Referring to FIGS. 1 and 2, the splicer contains a pair of splicer carriages 10, each of which contains a paper stop bar 11, cut-off knife 12 and splice sealing nip roll 13. A paper storage system 20, called the “dancer system,” allows paper to be fed to the corrugator on a continuous basis as the splice is made at zero speed. A splicer roll accelerator system called the “capstan roll” 30, creates higher tension levels to pull the paper roll up to speed. The corrugator speed at which the splice can be completed is determined by the performance of each of these features of the splicer.
The splicer carriage stop bar 11 clamps the tail of the expiring web 14. The more quickly the expiring roll web is brought to a full stop for splice seal, the faster the corrugator splicer speed. After the expiring paper roll web 14 is stopped, the pair of splice sealing nip rolls 13 in the splicer are brought together nipping the leading edge of the new paper roll web 15 that has been prepared with a suitable adhesive tape. After the nip rolls come together, the cutoff knife 12 fires causing the expired paper roll web 14 to be severed. The webs are then pulled through the splicer sealing nip rolls 13. Pulling forces are provided by the tension in the paper web 14, supplied by the downstream process.
This tension is amplified by the capstan roll system 30 located within the splicer down stream from the splicer carriage 10. The capstan system 30 is a roller that is driven to provide additional pull on the paper to accelerate the new paper roll to corrugator speed. This capstan roll can be powered in such a fashion as to slip under the paper wrapped around the roll or to simply add pull by virtue of torque applied to the capstan roll if the roll does not slip. If the capstan roll slips under the paper, the increase in paper tension upstream of the capstan roll is controlled by the capstan equation with ratio of tension out to tension in equal to the naperian logarithmic equation, eμβ where μ is the coefficient of friction of the paper to the capstan roll and β is the angle of wrap around the roll in radians. In the case of a 180° wrap and a coefficient of friction of 0.35, the slipping capstan roll amplifies the nominal web tension by a factor of 3. This creates higher pulling forces that accelerate the paper roll up to speed quickly allowing higher operating splicer speed.
The third splicer system affecting splicer speed is the dancer system 20. With more paper stored in the dancer system there is a longer time to accelerate the paper roll after the splice is complete and a higher operating splicer speed.
Splicer operating speeds have been increased with succeeding technology advancements in each of the splicer functions. The paper stop bar 11 was introduced to decrease time to stop the expiring paper web 14 in the splicer carriage 10. There is a limitation to the aggressiveness with which the clamp bar can be used due to the “brittleness” of the paper. An excessive clamping force can cause a paper break out.
In preparation for splicer setup, the corrugator operator presses the carriage back button to automatically position the splicer carriage 10 in front of the new paper roll 16. The paper from the new roll is pulled up over the idler roll 17, through the paper stop bar assembly 11, and over the splice sealing roll 13. The paper is pulled out until all wrinkles have been removed from the web, at which time the operator actuates a push-button, causing the paper stop bar 11 to positively hold the web in this position. Adhesive transfer tape is then applied to the leading edge of the new web. A slight edge lead-in is now trimmed on both sides of the web 15 and the paper is cut across using the cutting guide to ensure squareness. The tape backing is peeled away, leaving the web leading edge with a deposit of adhesive. The paper stop bar 11 is released and the sealing roll 13 is indexed back to accurately position the leading edge of the new web 15 for splicing. The paper stop bar is then actuated to positively hold the web in position until the instant the splice has been made. The operator presses the carriage in button, causing the splicer carriage 10 to be driven to a position close to the expiring corrugator web. With the carriage fully in, the operator rolls back the roll 16 to remove the slack between the roll and the carriage. The operator then actuates the brake set push-button. The splicer is then set up to perform the splice.
Classic splicer designs have used a steel capstan roll 30 with slightly more than 180° of wrap. These capstan designs have amplified paper tension by a factor of 3 to create larger paper roll acceleration forces. It was thought that resulting paper tension levels approached the threshold of safety required to avoid paper tear outs at splice.
Paper storage system capacity has been increased in various splicer designs to achieve higher splicer speeds. Early splicer designs had a single dancer roll. Subsequent designs evolved to a dual dancer roll 20, as shown in FIGS. 1 and 4. Splicer frame lengths were increased to achieve greater paper storage capacity, as shown in FIG. 5. Space in-line on the corrugator limited these designs, so quad dancer splicers were introduced, as shown in FIG. 6. The quad dancer splicer required more vertical space above the roll stands. In addition to the space limitation associated with these expanded paper storage concepts, a paper storage roller inertia problem became extreme with the quad dancer design. This problem was related to the fact that as the splice was initiated, the dancer assembly was powered forward, requiring dancer rollers to slow commensurately. Because of the dancer roller inertia, the dancer rolls would slip beneath the paper while slowing. This produced a multiplicative capstan effect that momentarily reduced web tension out of the splicer to near zero. This was followed by a high tension pulse as the dancer assembly speed stabilized. To solve this problem, dancer roll brakes and dancer carriage brakes were introduced. This complicated the design adding to the cost of the already expensive quad dancer splicer and creating a maintenance issue with a large number of friction brakes.
FIG. 4 shows a double dancer short side frame splicer capable of splicing at 650 FPM. FIG. 5 shows a double dancer longer side-frame splicer capable of splicing at 1000 FPM. Demand for higher splicing speeds has developed as higher corrugator operating speeds have been introduced. The requirement to slow the corrugator for splicing adversely affects board quality and offsets the productivity advantage of a higher corrugator operating speed. For this reason the quad dancer splicer shown in FIG. 6 was developed. This machine allows splicing at speeds up to 1300 FPM.